Current Conditions | ||
Temp | ![]() | 0.8 C |
RH | ![]() | 19 % |
Wind | ![]() | NE 13 mph |
Road | ![]() | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 341 FXHW60 PHFO 220632 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 832 PM HST Sat Apr 21 2018 .SYNOPSIS... High clouds moving northeastward within the subtropical jet stream will cover Maui and the Big Island tonight and Sunday. Trade showers are expected to decrease overnight, leading to drier weather across windward and mauka areas for Sunday. Another area of low level moisture will increase trade showers Monday night into Tuesday. Trade winds will become locally windy Monday into Tuesday, then slowly decline later in the week. A cold front may push down the chain with clouds and showers by next weekend. && .DISCUSSION... Trade wind weather will continue for the next several days as a strong surface high passes far north of the islands on Monday. This high will strengthen trade winds to locally windy levels across the area Monday through Tuesday. Wind speeds will gradually decrease after that and trade flow may possibly become disrupted starting Friday as a surface low passes far to the north. Models disagree on whether or not we will maintain light trades on Friday or if local diurnal winds will take over. By Friday night and Saturday, models show a late-season frontal boundary passing down the chain, with breezy trades returning afterwards. Thick middle and high clouds, associated with the subtropical jet, continue to cover Maui County and the Big Island, with Oahu and Kauai on the northern edge. Models keep this area around through Sunday. At lower levels, the back edge of an area of scattered to broken clouds and showers riding in on the trades is approaching the Big Island. This should lead to fewer windward and mauka showers later in the night and into Sunday for most of the state. Both GFS and ECMWF show another trade wind shower area arriving across windward Maui and the Big Island late Monday night or Tuesday. However, this week looks to be fairly quiet. Shower timing and placement on Friday will depend on how much trade flow is disrupted. However, expect an increase in showers Friday night into Saturday associated with the frontal boundary. && .AVIATION... A high pressure ridge north of the islands will continue to produce moderate to locally strong trade winds across the islands. An upper level jet stream will continue to produce moderate turbulence over the islands this evening. A stable atmosphere will keep VFR conditions in effect for most areas with lower ceilings and periods of scattered showers expected along windward slopes of each islands. AIRMET Sierra is in effect for tempo mountain obscuration over windward sections of Oahu, Molokai, Maui and the Big Island. Conditions are expected to remain in place overnight for most areas. AIRMET Tango remains in effect for moderate low level turbulence over and downwind of mountain ranges for all islands due to the moderate to breezy trade winds. Expect these conditions to continue through at least Sunday. Models show an area of moderate to severe upper level clear air turbulence over the islands, which is covered under SIGMET UNIFORM series. The forecast shows this area sticking around into Sunday, but weakening to moderate levels overnight. As this happens the SIGMET will be able to be dropped and could prompt another AIRMET Tango for moderate upper level turbulence over at least part of the local area. && .MARINE... Fresh to strong trades are forecast to hold through much of the upcoming week as high pressure remains established to the north. The small craft advisory currently in place for most marine areas from Oahu to the Big Island will hold through Sunday. This advisory will likely be extended and potentially expanded to other waters Monday through Wednesday as high pressure strengthens and a moderate northwest swell builds down the island chain boosting seas up to around the 10 ft mark. Rough surf is forecast to persist through the week along east facing shores due to fresh to strong trades holding in place locally and just upstream of the area. The best chance for advisory-level surf will come Tuesday through Thursday as the trades increase locally and expand farther upstream in response to 1030-1035 mb high building to the north. Although confidence remains low this far out in the forecast, there could be a break in the trades by Friday as a front moves into the area. A new northwest (320 deg) swell is expected to slowly fill in late Sunday afternoon, peak Monday, then slowly ease through midweek. This source is from a potent system that reached storm-force category Friday as it crossed the date line just south of the Aleutians between 40N and 50N (around 2000 miles northwest of the state). Surf is forecast to peak on Monday at heights below advisory levels along north and west facing shores. A reinforcing moderate northwest (330 deg) swell is forecast to fill in Thursday, peak Thursday night into Friday, then ease into the weekend. This reinforcement will be from a developing storm that is currently near the Kamchatka Peninsula and forecast to track east while skirting the Aleutian Islands Sunday through Wednesday. Surf associated with this feature should remain below advisory levels along north and west facing shores. A reinforcing southwest (220 deg) swell is forecast to fill in Monday and hold through midweek due to recent activity across the southern Pacific/Tasman Sea. Small to moderate surf will result along south facing shores each day. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel- Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Powell AVIATION...Bohlin MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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